One of the target searched by International Mobile Telecommunications (IMT)-Advanced system is the enhanced peak data rates to support advanced services and applications (100 Mbit/s for high mobility and 2 Gbit/s for low mobility were established as targets for research), as provided in [1] 3GPP TR 36.913 V8.0.0, “requirements for Further Advancements for E-UTRA (LTE-Advanced)”, Release 8, June 2008. Therefore, the LTE-Advanced system requires wider system bandwidth, e.g. up to 100 MHz, to achieve such high target peak data rates.
Carrier aggregation (CA) is a known approach to defining new bandwidth modes in fulfilling this requirement. Carrier aggregation has the advantages of not requiring extensive changes to the LTE physical layer structure, providing for bandwidth scalabilty and maintaining backwards compatibility, as provided in [2] 3GPP TSG-RAN WG1 Meeting #53b, R1-082448, “Carrier aggregation in Advanced E-UTRA”, Huawei and in [3] 3GPP TSG-RAN WG1 Meeting #53b, R1-082468, “Carrier aggregation in Advanced E-UTRA”, Ericsson. In CA systems, multiple component carriers (CC) are aggregated to cover the desired LTE-Advanced system bandwidth. These component carriers are either LTE- Rel-8 compatible or are designed specially to support new LTE-Advanced features. An LTE Rel-8 terminal can transmit data one of these component carriers, while an LTE-Advanced terminal can simultaneously transmit data on multiple component carriers.
Two user equipments scheduling approaches in carrier aggregation system are studied in] 3GPP TSG-RAN WG1 Meeting #57, R1-091828, “System Simulation Results on Carrier Aggregation for Bursty Traffic”, CMCC, namely independent carrier (IC) and carrier aggregation (CA).
In a first approach, known as independent carrier (IC), no change on the user equipments is required, i.e. the user equipments can receive data only on one of the carrier at a time and changing the carrier associated to the user equipment is a slow procedure. When a new user equipment attaches itself to a eNodeB (evolved Node B), the eNodeB assigns a suitable carrier to the new user equipment according to different criteria. The user equipment transmits data in the associated carrier frequency for a relatively long period of time until intra-frequency handover is performed.
One drawback of the IC approach is that it does not mention how to associate a user equipment to a component carrier. Furthermore, when large frequency gaps exist between the component carriers, the IC approach encounters difficulties in serving users equipment with optimal component carrier.
In a second approach, known as carrier aggregation (CA), a user equipment can simultaneously transmit on multiple carriers and no intra-frequency handover is required. The resource blocks which can be allocated on all the component carriers are allocated to the user equipments as a large resource pool. The user equipments can be scheduled to their best resources irrespective of whether or not these resources are within the same one or multiple component carriers(s).
One drawback of the CA approach is that is involves high scheduling complexity and requires multiple component carriers process ability on the user equipments side.